Composition and process for enhancing controlled free radical polymerization

ABSTRACT

The present invention relates to a composition and process for enhancing the controlled radical polymerization in the presence of nitroxyls and nitroxylethers by adding a chain transfer agent selected from the group consisting of mercaptanes, thioethers and disulfides to the polymerizable mixture. A further subject of the invention is the use of mercaptanes, thioethers and disulfides for increasing rate and yield of controlled radical polymerizations in the presence of a nitroxyl or a nitroxylether.

This is a divisional of application Ser. No. 10/381,223, filed Mar. 21,2003, now U.S. Pat. No. 7,074,860, which is a 371 of PCT/EP01/10782,filed Sep. 18, 2001.

U.S. Pat. No. 4,581,429 to Solomon et al., issued Apr. 8, 1986,discloses a free radical polymerization process which controls thegrowth of polymer chains to produce short chain or oligomerichomopolymers and copolymers, including block and graft copolymers. Thistype of polymerization is frequently called “living polymerization”. Theprocess employs an initiator having the formula (in part) R′R″N—O—X,where X is a free radical species capable of polymerizing unsaturatedmonomers. The reactions typically have low conversion rates.Specifically mentioned radical R′R″N—O● groups are derived from 1,1,3,3tetraethylisoin-doline, 1,1,3,3 tetrapropylisoindoline, 2,2,6,6tetramethylpiperidine, 2,2,5,5 tetramethyl-pyrrolidine ordi-t-butylamine.

U.S. Pat. No. 5,322,912 to Georges et al. issued Jun. 21, 1994 disclosesa polymerization process using a free radical initiator, a polymerizablemonomer compound and a stable free radical agent of the basic structureR′R″N—O● for the synthesis of homopolymers and block copolymers.

EP 0 759 039 to Georges et al. describes the improved polymerization ofacrylates using 4-oxo-2,2,6,6-tetramethyl-1-piperidinyloxy free radicalas stable free radical agent R′R″N—O●.

However, the suggested compounds do not fulfill all requirements.Particularly the polymerization of acrylates does not proceed fastenough and/or the monomer to polymer conversion is not as high asdesired.

For this reason many attempts have been made in the last years toimprove conversion rate whilst retaining the advantages of controlledpolymerization such as for example low polydispersity and the capabilityof block copolymer formation. Many improvements have been made bymodifying the chemical structure of the nitroxyl radical or of thenitroxyl ether.

WO 98/13392 for example describes open chain alkoxyamine compounds whichhave a symmetrical substitution pattern and are derived from NO gas orfrom nitroso compounds.

WO 96/24620 describes a polymerization process in which very specificstable free radical agents are used, such as for example

WO 98/30601 discloses specific nitroxyls based on imidazolidinons.

WO 98/44008 discloses specific nitroxyls based on morpholinones,piperazinones and piperazindiones.

Despite the above mentioned structural attempts to improve controlledradical polymerization reactions there is still a need for improving thepolymerization process to obtain higher yields in shorter reactiontimes.

EP-A-735 052 for example discloses a method for preparing thermoplasticpolymers of narrow polydispersitiy by free radical-initatedpolymerization, which comprises adding a free radical initiator, astable free radical agent and a pyridinium tosylate to a styrenemonomer, which enhances the reaction time and conversion rate of thepolymerization.

Other accelerators such as phosphonic and sulfonic acids are describedin WO 96/18663, phosphites are described in U.S. Pat. No. 5,610,249 andprotonic acids are described in U.S. Pat. No. 5,322,912.

Surprisingly it has now been found that the rate of polymerization andconversion can be strongly improved by adding to the polymerizablemixture a chain transfer agent selected from the group consisting of amercaptane, a thioether or a disulfide. Higher molecular weights arereached in shorter reaction times whilst polydispersity remains low andsurprisingly the polymers can be completely reinitiated to form blockcopolymers. This is surprising, since one would expect that at leastpartially terminated polymers (not anymore “living” polymers) areformed.

Moreover when reinitiating a polymer, which has been prepared viacontrolled radical polymerization in the presence of a nitroxyl radicalor a nitroxyl ether, to form block copolymers also a remarkable increasein rate and conversion of block copolymer formation is observed whensaid chain transfer agents are added to the block copolymerization step.

The low polydispersity which is characteristic for controlled radicalpolymerizations remains essentially unaffected by the addition of saidchain transfer agents.

The polymerization processes and resin products of the present inventionare useful in many applications, including a variety of specialtyapplications, such as for the preparation of block copolymers and/orgraft copolymers which are useful as compatibilizing agents for polymerblends or dispersing agents for coating systems.

Polymers prepared by nitroxyl radical or nitroxyl ether mediated radicalpolymerization exhibit sometimes a yellow/brown color. Surprisingly ithas been found that the presence of the chain transfer agent in thepolymerizable composition is in many cases also beneficial for the colorof the final polymer.

One subject of the present invention is a polymerizable composition,comprising

a) at least one ethylenically unsaturated monomer or oligomer, and

b1) at least one nitroxyl ether having the structural element

whereinX represents a group having at least one carbon atom and is such thatthe free radical X● derived from X is capable of initiatingpolymerization of ethylenically unsaturated monomers; orb2) at least one stable free nitroxyl radical

and a free radical initiator andc) a chain transfer agent selected from the group consisting of amercaptane, a thioether and a disulfide, with the proviso, that, if astable free nitroxyl radical is present, the chain transfer agent is nota disulfide.

Also subject of the invention is a polymerizable composition, comprising

a) a macroinitiator, which is a oligomer or polymer prepared in thepresence of a nitroxyl radical or a nitroxyl ether and having attachedto the oligomer/polymer backbone a nitroxyl group with the structuralelement

b) an ethylenically unsaturated monomer or oligomer andc) a chain transfer agent selected from the group consisting of amercaptane, a thioether and a disulfide.

The macroinitiator can be prepared by polymerizing a monomer in thepresence of a nitroxyl or nitroxyl ether or by grafting of an existingconventionally polymerized polymer with a nitroxyl ether or a nitroxylradical, as described in EP-A-1 115 766 or EP-A-1 115 765.

An ethylenically unsaturated oligomer is for example apoloyethylenglykoldiacrylate or in general a oligomer which has beenfunctionalized at the end groups. Such oligomers are known and largelyitems of commerce.

Preferably the ethylenically unsaturated monomer is selected from thegroup consisting of ethylene, propylene, n-butylene, i-butylene,styrene, substituted styrene, conjugated dienes, acrolein, vinylacetate, vinylpyrrolidone, vinylimidazole, maleic anhydride,(alkyl)acrylic acidanhydrides, (alkyl)acrylic acid salts, (alkyl)acrylicesters, (alkyl)acrylonitriles, (alkyl)acrylamides, vinyl halides orvinylidene halides.

Preferably the ethylenically unsaturated monomer is a compound offormula

CH₂═C(R_(a)—(C=Z)-R_(b), wherein R_(a) is hydrogen or C₁-C₄alkyl, R_(b)is NH₂, O⁻(Me⁺), glycidyl, unsubstituted C₁-C₁₈alkoxy, C₂-C₁₀₀alkoxyinterrupted by at least one N and/or O atom, or hydroxy-substitutedC₁-C₁₈alkoxy, unsubstituted C₁-C₁₈alkylamino, di(C₁-C₁₈alkyl)amino,hydroxy-substituted C₁-C₁₈alkylamino or hydroxy-substituteddi(C₁-C₁₈alkyl)amino, —O—CH₂—CH₂—N(CH₃)₂ or —O—CH₂—CH₂—N⁺H(CH₃)₂ An⁻;An⁻ is a anion of a monovalent organic or inorganic acid;Me is a monovalent metal atom or the ammonium ion.Z is oxygen or sulfur.

Examples of acids from which the anion An⁻ is derived are C₁-C₁₂carboxylic acids, organic sulfonic acids such as CF₃SO₃H or CH₃SO₃H,mineralic acids such as HCI, HBr or HI, oxo acids such as HClO₄ orcomplex acids such as HPF₆ or HBF₄.

Examples for R_(a) as C₂-C₁₀₀alkoxy interrupted by at least one O atomare of formula

wherein R_(c) is C₁-C₂₅alkyl, phenyl or phenyl substituted byC₁-C₁₈alkyl, R_(d) is hydrogen or methyl and v is a number from 1 to 50.These monomers are for example derived from non ionic surfactants byacrylation of the corresponding alkoxylated alcohols or phenols. Therepeating units may be derived from ethylene oxide, propylene oxide ormixtures of both.

Further examples of suitable acrylate or methacrylate monomers are givenbelow.

An⁻, wherein An⁻ and R_(a) have the meaning as defined above and R_(e)is methyl or benzyl. An⁻ is preferably Cl⁻, Br⁻ or ⁻O₃S—CH₃.

Further acrylate monomers are

Examples for suitable monomers other than acrylates are

Preferably R_(a) is hydrogen or methyl, R_(b) is NH₂, gycidyl,unsubstituted or with hydroxy substituted C₁-C₄alkoxy, unsubstitutedC₁-C₄alkylamino, di(C₁-C₄alkyl)amino, hydroxy-substitutedC₁-C₄alkylamino or hydroxy-substituted di(C₁-C₄alkyl)amino; and

Z is oxygen.

More preferred the ethylenically unsaturated monomer is an acrylic acidester, acrylamide, acrylnitrile, methacrylic acid ester, methacrylamide,methacrylnitrile.

Acrylic acid esters and methacrylic acid esters are typically C₁-₁₈alkylesters.

Most preferred is n-butylacrylate, tert-butylacrylate, methylacrylate,ethylacrylate, propylacrylate, hexylacrylate and hydroxyethylacrylate.

The nitroxyl ethers and nitroxyl radicals are principally known fromU.S. Pat. No. 4,581,429 or EP-A-621 878. Particularly useful are theopen chain compounds described in WO 98/13392, WO 99/03894 and WO00/07981, the piperidine derivatives described in WO 99/67298 and GB2335190 or the heterocyclic compounds described in GB 2342649 and WO96/24620. Preferably the nitroxyl ether of component b1) is of formulaA, B or O,

whereinm is 1,R is hydrogen, C₁-C₁₈alkyl which is uninterrupted or interrupted by oneor more oxygen atoms, cyanoethyl, benzoyl, glycidyl, a monovalentradical of an aliphatic carboxylic acid having 2 to 18 carbon atoms, ofa cycloaliphatic carboxylic acid having 7 to 15 carbon atoms, or anα,β-unsaturated carboxylic acid having 3 to 5 carbon atoms or of anaromatic carboxylic acid having 7 to 15 carbon atoms;p is 1;R₁₀₁ is C₁-C₁₂alkyl, C₅-C₇cycloalkyl, C₇-C₈aralkyl, C₂-C₁₈alkanoyl,C₃-C₅alkenoyl or benzoyl;R₁₀₂ is C₁-C₁₈alkyl, C₅-C₇cycloalkyl, C₂-C₈alkenyl unsubstituted orsubstituted by a cyano, carbonyl or carbamide group, or is glycidyl, agroup of the formula —CH₂CH(OH)-Z or of the formula —CO-Z or —CONH-Zwherein Z is hydrogen, methyl or phenyl;G₆ is hydrogen and G₅ is hydrogen or C₁-C₄alkyl,G₁ and G₃ are methyl and G₂ and G₄ are ethyl or propyl or G₁ and G₂ aremethyl and G₃ and G₄ are ethyl or propyl; andX is selected from the group consisting of —CH₂-phenyl, CH₃CH-phenyl,(CH₃)₂C-phenyl, (C₅-C₆cycloalkyl)₂CCN, (CH₃)₂CCN, —CH₂CH═CH₂,CH₃CH—CH═CH₂ (C₁-C₄alkyl)CR₂₀—C(O)-phenyl,(C₁-C₄)alkyl-CR₂₀—C(O)—(C₁-C₄)alkoxy,(C₁-C₄)alkyl-CR₂₀—C(O)—(C₁-C₄)alkyl,(C₁-C₄)alkyl-CR₂₀—C(O)—N-di(C₁-C₄)alkyl,(C₁-C₄)alkyl-CR₂₀—C(O)—NH(C₁-C₄)alkyl, (C₁-C₄)alkyl-CR₂₀—C(O)—NH₂,whereinR₂₀ is hydrogen or (C₁-C₄)alkyl.

More preferably in formula A, B and O

R is hydrogen, C₁-C₁₈alkyl, cyanoethyl, benzoyl, glycidyl, a monovalentradical of an aliphatic, carboxylic acid;

R₁₀₁ is C₁-C₁₂alkyl, C₇-C₈aralkyl, C₂-C₁₈alkanoyl, C₃-C₅alkenoyl orbenzoyl;

R₁₀₂ is C₁-C₁₈alkyl, glycidyl, a group of the formula —CH₂CH(OH)-Z or ofthe formula —CO-Z,

wherein Z is hydrogen, methyl or phenyl; and

X is CH₃—CH-phenyl.

The above compounds and their preparation are described in GB 2335190.

Another preferred group of nitroxyl ethers of component b1) are those offormula (Ic), (Id), (Ie), (If), (Ig) or (Ih)

wherein R₁, R₂, R₃ and R₄ independently of each other are C₁-C₁₈alkyl,C₃-C₁₈alkenyl, C₃-C₁₈alkinyl, C₁-C₁₈alkyl, C₃-C₁₈alkenyl, C₃-C₁₈alkinylwhich are substituted by OH, halogen or a group —O—C(O)—R₅, C₂-C₁₈alkylwhich is interrupted by at least one O atom and/or NR₅ group,C₃-C₁₂cycloalkyl or C₆-C₁₀aryl or R₁ and R₂ and/or R₃ and R₄ togetherwith the linking carbon atom form a C₃-C₁₂cycloalkyl radical;R₅, R₆ and R₇ independently are hydrogen, C₁-C₁₈alkyl or C₆-C₁₀aryl;R₈ is hydrogen, OH, C₁-C₁₈alkyl, C₃-C₁₈alkenyl, C₃-C₁₈alkinyl,C₁-C₁₈alkyl, C₃-C₁₈alkenyl, C₃-C₁₈alkinyl which are substituted by oneor more OH, halogen or a group —O—C(O)—R₅, C₂-C₁₈alkyl which isinterrupted by at least one O atom and/or NR₅ group, C₃-C₁₂cycloalkyl orC₆-C₁₀aryl C₇-C₉phenylalkyl, C₅-C₁₀heteroaryl, —C(O)—C₁-C₁₈alkyl,—O—C₁-C₁₈alkyl or —COOC₁-C₁₈alkyl;R₉, R₁₀, R₁₁, and R₁₂ are independently hydrogen, phenyl or C₁-C₁₈alkyl;andX is selected from the group consisting of —CH₂-phenyl, CH₃CH-phenyl,(CH₃)₂C-phenyl, (C₅-C₆cycloalkyl)₂CCN, (CH₃)₂CCN, —CH₂CH═CH₂,CH₃CH—CH═CH₂ (C₁-C₄alkyl)CR₂₀—C(O)-phenyl,(C₁-C₄)alkyl-CR₂₀—C(O)—(C₁-C₄)alkoxy,(C₁-C₄)alkyl-CR₂₀—C(O)—(C₁-C₄)alkyl,(C₁-C₄)alkyl-CR₂₀—C(O)—N-di(C₁-C₄)alkyl,(C₁-C₄)alkyl-CR₂₀—C(O)—NH(C₁-C₄)alkyl, (C₁-C₄)alkyl-CR₂₀—C(O)—NH₂,whereinR₂₀ is hydrogen or (C₁-C₄)alkyl.

More preferably in formula (Ic), (Id), (Ie), (f), (Ig) and (Ih) at leasttwo of R₁, R₂, R₃ and R₄ are ethyl, propyl or butyl and the remainingare methyl; or

R₁ and R₂ or R₃ and R₄ together with the linking carbon atom form aC₅-C₆cycloalkyl radical and one of the remaining substituents is ethyl,propyl or butyl.

Most preferably X is CH₃CH-phenyl.

The above compounds and their preparation is described in GB 2342649.

When a nitroxyl radical is used together with a free radical initiator,the nitroxyl radical of component b2) is preferably of formula A′, B′ orO′,

whereinm is 1,R is hydrogen, C₁-C₁₈alkyl which is uninterrupted or interrupted by oneor more oxygen atoms, cyanoethyl, benzoyl, glycidyl, a monovalentradical of an aliphatic carboxylic acid having 2 to 18 carbon atoms, ofa cycloaliphatic carboxylic acid having 7 to 15 carbon atoms, or anα,βunsaturated carboxylic acid having 3 to 5 carbon atoms or of anaromatic carboxylic acid having 7 to 15 carbon atoms;p is 1;R₁ is C₁-C₁₂alkyl, C₅-C₇cycloalkyl, C₂-C₁₈aralkyl, C₂-C₈alkanoyl,C₃-C₅alkenoyl or benzoyl;R₂ is C₁-C₁₈alkyl, C₅-C₇alkyl, C₂-C₈alkenyl unsubstituted or substitutedby a cyano, carbonyl or carbamide group, or is glycidyl, a group of theformula —CH₂CH(OH)-Z or of the formula —CO-Z or —CONH-Z wherein Z ishydrogen, methyl or phenyl;G₆ is hydrogen and G₅ is hydrogen or C₁-C₄alkyl, andG₁ and G₃ are methyl and G₂ and G₄ are ethyl or propyl or G₁ and G₂ aremethyl and G₃ and G₄ are ethyl or propyl.

More preferably in formula A′, B′ and O′

R is hydrogen, C₁-C₁₈alkyl, cyanoethyl, benzoyl, glycidyl, a monovalentradical of an aliphatic, carboxylic acid;

R₁ is C₁-C₁₂alkyl, C₇-C₈aralkyl, C₂-C₁₈alkanoyl, C₃-C₅alkenoyl orbenzoyl;

R₂ is C₁-C₁₈alkyl, glycidyl, a group of the formula —CH₂CH(OH)-Z or ofthe formula —CO-Z, wherein Z is hydrogen, methyl or phenyl.

The above compounds and their preparation are described in GB 2335190.

Another preferred group of nitroxyl radicals are those of formula (Ic′),(Id′), (Ie′), (If′), (Ig′) or (Ih′)

wherein R₁, R₂, R₃ and R₄ independently of each other are C₁-C₁₈alkyl,C₃-C₁₈alkenyl, C₃-C₁₈alkinyl, C₁-C₁₈alkyl, C₃-C₁₈alkenyl, C₃-C₁₈alkinylwhich are substituted by OH, halogen or a group —O—C(O)—R₅, C₂-C₁₈alkylwhich is interrupted by at least one O atom and/or NR₅ group,C₃-C₁₂cycloalkyl or C₆-C₁₀aryl or R₁ and R₂ and/or R₃ and R₄ togetherwith the linking carbon atom form a C₃-C₁₂cycloalkyl radical;R₅, R₆ and R₇ independently are hydrogen, C₁-C₁₈alkyl or C₆-C₁₀aryl;R₆ is hydrogen, OH, C₁-C₁₈alkyl, C₃-C₁₈alkenyl, C₃-C₁₈alkinyl,C₁-C₁₈alkyl, C₃-C₁₈alkenyl, C₃-C₁₈alkinyl which are substituted by oneor more OH, halogen or a group —O—C(O)—R₅, C₂-C₁₈alkyl which isinterrupted by at least one O atom and/or NR₅ group, C₃-C₁₂cycloalkyl orC₆-C₁₀aryl, C₇-C₉phenylalkyl, C₅-C₁₀heteroaryl, —C(O)—C₁-C₁₈alkyl,—O—C₁-C₁₈alkyl or —COOC₁-C₁₈alkyl; andR₉, R₁₀, R₁₁, and R₁₂ are independently hydrogen, phenyl or C₁-C₁₈alkyl.

More preferably in formula (Ic′), (Id′), (Ie′), (If′), (Ig′) and (Ih′)at least two of R₁, R₂, R₃ and R₄ are ethyl, propyl or butyl and theremaining are methyl; or

R₁ and R₂ or R₃ and R₄ together with the linking carbon atom form aC₅-C₆cycloalkyl radical and one of the remaining substituents is ethyl,propyl or butyl.

The above compounds and their preparation is described in GB 2342649.

The structural element

attached to the polymer backbone of the macroinitiator is preferablyderived from a compound of formulae A, B, O (A′, B′, O′) or of formulaeIc, Id, Ie, If, Ig, Ih (Ic′, Id′, Ie′, If′, Ig′, Ih′).

Further preferences given above for the nitroxyl ether and nitroxylradical apply also for the nitroxyl moiety attached to the polymerbackbone of the macroinitiator.

The alkyl radicals in the various substituents may be linear orbranched. Examples of alkyl containing 1 to 18 carbon atoms are methyl,ethyl, propyl, isopropyl, butyl, 2-butyl, isobutyl, t-butyl, pentyl,2-pentyl, hexyl, heptyl, octyl, 2-ethylhexyl, t-octyl, nonyl, decyl,undecyl, dodecyl, tridecyl, tetradecyl, hexadecyl and octadecyl.

Alkenyl with 3 to 18 carbon atoms is a linear or branched radical as forexample propenyl, 2-butenyl, 3-butenyl, isobutenyl, n-2,4-pentadienyl,3-methyl-2-butenyl, n-2-octenyl, n-2-dodecenyl, iso-dodecenyl, oleyl,n-2-octadecenyl oder n-4-octadecenyl. Preferred is alkenyl with 3 bis12, particularly preferred with 3 to 6 carbon atoms.

Alkinyl with 3 to 18 is a linear or branched radical as for examplepropinyl (—CH₂—C≡CH), 2-butinyl, 3-butinyl, n-2-octinyl, odern-2-octadecinyl. Preferred is alkinyl with 3 to 12, particularlypreferred with 3 to 6 carbon atoms.

Examples for hydroxy substituted alkyl are hydroxy propyl, hydroxy butylor hydroxy hexyl.

Examples for halogen substituted alkyl are dichloropropyl,monobromobutyl or trichlorohexyl.

C₂-C₁₈alkyl interrupted by at least one O atom is for example—CH₂—CH₂—O—CH₂—CH₃, —CH₂—CH₂—O—CH₃— or—CH₂—CH₂—O—CH₂—CH₂—CH₂—O—CH₂—CH₃—. It is preferably derived frompolyethlene glycol. A general description is —((CH₂)_(a)—O)_(b)—H/CH₃,wherein a is a number from 1 to 6 and b is a number from 2 to 10.

C₂-C₁₈alkyl interrupted by at least one NR₅ group may be generallydescribed as —((CH₂)_(a)—NR₅)_(b)—H/CH₃, wherein a, b and R₅ are asdefined above.

C₃-C₁₂cycloalkyl is typically, cyclopropyl, cyclopentyl,methylcyclopentyl, dimethylcyclopentyl, cyclohexyl, methylcyclohexyl ortrimethylcyclohexyl.

C₆-C₁₀ aryl is for example phenyl or naphthyl, but also comprised areC₁-C₄alkyl substituted phenyl, C₁-C₄alkoxy substituted phenyl, hydroxy,halogen or nitro substituted phenyl. Examples for alkyl substitutedphenyl are ethylbenzene, toluene, xylene and its isomers, mesitylene orisopropylbenzene. Halogen substituted phenyl is for exampledichlorobenzene or bromotoluene.

Alkoxy substituents are typically methoxy, ethoxy, propoxy or butoxy andtheir corresponding isomers.

C₇-C₉phenylalkyl is benzyl, phenylethyl or phenylpropyl.

C₅-C₁₀heteroaryl is for example pyrrol, pyrazol, imidazol, 2,4,dimethylpyrrol, 1-methylpyrrol, thiophene, furane, furfural, indol,cumarone, oxazol, thiazol, isoxazol, isothiazol, triazol, pyridine,α-picoline, pyridazine, pyrazine or pyrimidine.

If R is a monovalent radical of a carboxylic acid, it is, for example,an acetyl, propionyl, butyryl, valeroyl, caproyl, stearoyl, lauroyl,acryloyl, methacryloyl, benzoyl, cinnamoyl orβ-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl radical.)

C₁-C₁₈alkanoyl is for example, formyl, propionyl, butyryl, octanoyl,dodecanoyl but preferably acetyl and C₃-C₅alkenoyl is in particularacryloyl.

Particularly suitable nitroxyl ethers and nitroxyl radicals are those offormulae

The free radical initiator of component b2) is preferably a bis-azocompound, a peroxide perester or a hydroperoxide.

Specific preferred radical sources are 2,2′-azobisisobutyronitrile,2,2′-azobis(2-methyl-butyronitrile),2,2′-azobis(2,4-dimethylvaleronitrile),2,2′-azobis(4-methoxy-2,4-dimethylvale-ronitrile),1,1′-azobis(1-cyclohexanecarbonitrile), 2,2′-azobis(isobutyramide)dihydrate, 2-phenylazo-2,4-dimethyl-4-methoxyvaleronitrile,dimethyl-2,2′-azobisisobutyrate, 2-(carbamoylazo)isobutyronitrile,2,2′-azobis(2,4,4-trimethylpentane), 2,2′-azobis(2-methylpropane),2,2′-azobis(N,N′-dimethyleneisobutyramidine), free base orhydrochloride, 2,2′-azobis(2-amidinopropane), free base orhydrochloride,2,2′-azobis{2-methyl-N-[1,1-bis(hydroxymethyl)ethyl]propionamide} or2,2′-azobis(2-methyl-N-[1,1-bis(hydroxymethyl)-2-hydroxyethyl]propionamide;acetyl cyclohexane sulphonyl peroxide, diisopropyl peroxy dicarbonate,t-amyl perneodecanoate, t-butyl perneodecanoate, t-butyl perpivalate,t-amylperpivalate, bis(2,4-dichlorobenzoyl)peroxide, diisononanoylperoxide, didecanoyl peroxide, dioctanoyl peroxide, dilauroyl peroxide,bis (2-methylbenzoyl) peroxide, disuccinic acid peroxide, diacetylperoxide, dibenzoyl peroxide, t-butyl per 2-ethylhexanoate,bis-(4-chlorobenzoyl)-peroxide, t-butyl perisobutyrate, t-butylperisobutyrate, 1,1-bis(t-butylperoxy)3,5,5-trimethylcyclohexane,1,1-bis(t-butylperoxy)cyclohexane, t-butyl peroxy isopropyl carbonate,t-butyl perisononaoate, 2,5-dimethylhexane 2,5-dibenzoate, t-butylperacetate, t-amyl perbenzoate, t-butyl perbenzoate, 2,2-bis(t-butylperoxy) butane, 2,2 bis (t-butylperoxy) propane, dicumylperoxide, 2,5-dimethylhexane-2,5-di-t-butylperoxide, 3-t-butylperoxy3-phenylphthalide, di-t-amyl peroxide, α, α′-bis(t-butylperoxyisopropyl) benzene, 3,5-bis (t-butylperoxy)3,5-dimethyl 1,2-dioxolane,di-t-butyl peroxide, 2,5-dimethylhexyne-2,5-di-t-butylperoxide,3,3,6,6,9,9-hexamethyl 1,2,4,5-tetraoxa cyclononane, p-menthanehydroperoxide, pinane hydroperoxide, diisopropylbenzenemono-α-hydroperoxide, cumene hydroperoxide or t-butyl hydroperoxide.

Azo initiators and peroxides are most preferred.

Preferably component c) is a compound of formula (IIa), (IIb) or (IIc)R₃₀—S—H (IIa), R₃₀—S—R₃₀ (IIb), R₃₁—S—S—R₃₁ (IIc) whereinR₃₀ is C₁-C₁₈alkyl, C₃-C₁₈ alkenyl, C₃-C₁₈alkinyl,(C₁-C₁₈)alkyl-O—(C₁-C₁₈alkylen)-,HO—(C₁-C₁₈alkylen)-, (C₁-C₁₈alkyl)₂N—(C₁-C₁₈alkylen)-,(C₁-C₁₈)alkyl-O—C(O)—(C₁-C₁₈alkylen)-, phenyl, phenyl(C₁-C₃alkyl),phenyl-C(O)— or (C₁-C₁₈alkyl)₂N—C(S)—; andR₃₁ is C₁-C₁₈alkyl, C₃-C₁₈ alkenyl, C₃-C₁₈alkinyl,(C₁-C₁₈)alkyl-O—(C₁-C₁₈alkylen)-,HO—(C₁-C₁₈alkylen)-.

Particularly preferred is a compound of formula (IIa), (IIb) or (IIc)wherein R₃₀ and R₃, is C₁-C₁₈alkyl.

Specific compounds are mercaptoethanol, dodecylmercaptane,dibenzylsufide, dibutyl-sulfide, octadecyldisulfide,distearylthiodipropionate (Irganox PS 802),dipalmityldithiodipropionate, dilaurylthiodipropionate (Irganox® PS800).

More preferably component c) is of formula (IIa) and R₃₀ is C₈-C₁₈alkyl.

Most preferred is dodecylmercaptane.

Chain transfer agents are known and for example described in “TheChemistry of Free Radical Polymerization”, Ed. G. Moad, E. Rizzardo,Pergamon 1995, pages 234-251. They are largely items of commerce.

In contrast to so called “iniferters” (initiator-transferagent-terminator), chain transfer agents are not used alone without aradical initiator. They do not per se sufficiently initiatepolymerization. A definition and examples for “iniferters” are given byT. Otsu, A. Matsumoto in Adv. Polym. Sci. 1998, 136, 75-137.

A further subject of the invention is a process for preparing anoligomer, a cooligomer, a polymer or a copolymer (block, random orgraft) by free radical polymerization of at least one ethylenicallyunsaturated monomer or oligomer, which comprises (co)polymerizing themonomer or monomers/oligomers in the presence of

b1) at least one nitroxyl ether having the structural element

under reaction conditions capable of effecting scission of the O—X bondto form two free radicals, the radical ●X being capable of initiatingpolymerization; orb2) at least one stable free nitroxyl radical

and a free radical initiator andc) a chain transfer agent selected from the group consisting of amercaptane, a thioether and a disulfide, with the proviso, that, if astable free nitroxyl radical is present, the chain transfer agent is nota disulfide.

Also subject of the invention is a process for preparing a block(co)polymer by free radical polymerization which comprises(co)polymerizing

a) a macroinitiator, which is a oligomer or polymer prepared by radicalpolymerization in the presence of a nitroxyl radical or a nitroxyl etherand having attached to the oligomer/polymer backbone a nitroxyl groupwith the structural element

b) an ethylenically unsaturated monomer or oligomer in the presence ofc) a chain transfer agent selected from the group consisting of amercaptane, a thioether and a disulfide; under reaction conditionscapable of effecting scission of the O-polymer bond to form two freeradicals, the polymer radical (macroinitiator) being capable ofinitiating polymerization.

Definitions and preferences for the components have already been givenabove.

Preferably the nitroxyl ether of component b1) or the nitroxyl radicalof component b2) is present in an amount of from 0.001 mol-% to 20mol-%, more preferably of from 0.002 mol-% to 10 mol-% and mostpreferably of from 0.005 mol-% to 5 mol-% based on the monomer ormonomer mixture.

Preferably the free radical initiator is present in an amount of 0.001mol-% to 20 mol-%, based on the monomer or monomer mixture.

The molar ratio of free radical initiator to stable free nitroxylradical is preferably from 20:1 to 1:2, more preferably from 10:1 to1:2.

Scission of the O—X bond or of the O-polymer bond of the nitroxyl etheror of the macroinitiator may be effected by ultrasonic treatment,radiation with actinic light or heating.

The scission of the O—X bond or of the O-polymer bond is preferablyeffected by heating and takes place at a temperature of between 50° C.and 180° C., more preferably from 80° C. to 145° C.

Preferably the chain transfer agent, component c), is present in anamount of from 0.001 mol-% to 0,5 mol-%, more preferably of from 0.001mol-% to 0,3 mol-% and most preferably of from 0.001 mol-% to 0,25mol-%, based on the monomer or monomer mixture.

The molar ratio of stable free nitroxyl radical or nitroxyl ether tochain transfer agent is preferably from 100:1 to 4:1.

After the polymerization step is completed the reaction mixture may becooled down to a temperature below 60° C., preferably to roomtemperature. The polymer may be stored at this temperature withoutfurther reactions occuring.

The process may be carried out in the presence of an organic solvent orin the presence of water or in mixtures of organic solvents and water.Additional cosolvents or surfactants, such as glycols or ammonium saltsof fatty acids, may be present. Other suitable cosolvents are describedhereinafter.

If organic solvents are used, suitable solvents or mixtures of solventsare typically pure alkanes (hexane, heptane, octane, isooctane),aromatic hydrocarbons (benzene, toluene, xylene), halogenatedhydrocarbons (chlorobenzene), alkanols (methanol, ethanol, ethyleneglycol, ethylene glycol monomethyl ether), esters (ethyl acetate,propyl, butyl or hexyl acetate) and ethers (diethyl ether, dibutylether, ethylene glycol dimethyl ether), or mixtures thereof.

The aqueous polymerization reactions can be supplemented with awater-miscible or hydrophilic cosolvent to help ensure that the reactionmixture remains a homogeneous single phase throughout the monomerconversion. Any water-soluble or water-miscible cosolvent may be used,as long as the aqueous solvent medium is effective in providing asolvent system which prevents precipitation or phase separation of thereactants or polymer products until after all polymerization reactionshave been completed. Exemplary cosolvents useful in the presentinvention may be selected from the group consisting of aliphaticalcohols, glycols, ethers, glycol ethers, pyrrolidines, N-alkylpyrrolidinones, N-alkyl pyrrolidones, polyethylene glycols,polypropylene glycols, amides, carboxylic acids and salts thereof,esters, organosulfides, sulfoxides, sulfones, alcohol derivatives,hydroxyether derivatives such as butyl carbitol or cellosolve, aminoalcohols, ketones, and the like, as well as derivatives thereof andmixtures thereof. Specific examples include methanol, ethanol, propanol,dioxane, ethylene glycol, propylene glycol, diethylene glycol, glycerol,dipropylene glycol, tetrahydrofuran, and other water-soluble orwater-miscible materials, and mixtures thereof. When mixtures of waterand water-soluble or water-miscible organic liquids are selected as theaqueous reaction media, the water to cosolvent weight ratio is typicallyin the range of about 100:0 to about 10:90.

The process is particularly useful for the preparation of blockcopolymers.

Block copolymers are, for example, block copolymers of polystyrene andpolyacrylate (e.g., poly(styrene-co-acrylate) orpoly(styrene-co-acrylate-co-styrene). They are useful as adhesives or ascompatibilizers for polymer blends or as polymer toughening agents.Poly(methylmethacrylate-co-acrylate) diblock copolymers orpoly(methylacrylate-co-acrylate-co-methacrylate) triblock copolymers)are useful as dispersing agents for coating systeme, as coatingadditives (e.g. rheological agents, compatibilizers, reactive diluents)or as resin component in coatings(e.g. high solid paints). Blockcopolymers of styrene, (meth)acrylates and/or acrylonitrile are usefulas modifiers for plastics, elastomers and adhesives.

Furthermore, block copolymers of this invention, wherein the blocksalternate between polar monomers and non-polar monomers, are useful inmany applications as amphiphilic surfactants or dispersants forpreparing highly uniform polymer blends.

The (co)polymers of the present invention may have a number averagemolecular weight from 1 000 to 400 000 g/mol, preferably from 2 000 to250 000 g/mol and, more preferably, from 2 000 to 200 000 g/mol. Thenumber average molecular weight may be determined by size exclusionchromatography (SEC), matrix assisted laser desorption/ionization massspectrometry (MALDI-MS) or, if the initiator carries a group which canbe easily distinguished from the monomer(s), by NMR spectroscopy orother conventional methods.

The polymers or copolymers of the present invention have preferably apolydispersity of from 1.1 to 2, more preferably of from 1.2 to 1.8.

Thus, the present invention also encompasses in the synthesis novelblock, multi-block, star, gradient, random, hyperbranched and dendriticcopolymers, as well as graft copolymers.

The polymers prepared by the present invention are useful for followingapplications: adhesives, detergents, dispersants, emulsifiers,surfactants, defoamers, adhesion promoters, corrosion inhibitors,viscosity improvers, lubricants, rheology modifiers, thickeners,crosslinkers, paper treatment, water treatment, electronic materials,paints, coatings, photography, ink materials, imaging materials,superabsorbants, cosmetics, hair products, preservatives, biocidematerials or modifiers for asphalt, leather, textiles, ceramics andwood.

The following examples illustrate the invention.

Compounds Used

The nitroxyl ether compound (101) and (102) are prepared according to GB2335190

Compound 102 is the compound of example 7 in GB 2335190. Compound 101 isthe 4-acetylester of compound 102 and can be prepared from compound 101by standard methods.

n-butylacrylate and tert.-butylacrylate are commercially available forexample from Merck. 1-dodecylmercaptane and ethylhexylthioglycolate arecommercially available from Aldrich and WAKO.

EXAMPLES E1 to E3

In an evacuated Schlenk tube, flushed with argon and equipped withmagnetic stirrer, the amount of nitroxyl ether and dodecylmercaptanegiven in Table 1 is added to 0.436 mol freshly distilled n-butylacrylateunder an argon atmosphere. The Schlenk tube is closed and the remainingoxygen is removed in two freeze thaw cycles with liquid nitrogen. Thetube is filled with argon and heated to 120° C. for 6 hours withstirring. The remaining monomer is removed under vacuum at roomtemperature. Drying is continued until constant weight of the residue.Molecular weight and distribution are determined using size exclusionchromatography with tetrahydrofurane and calibrated with polystyrenestandards. The results are given in Table 1.

TABLE 1 Influence of dodecylmercaptane on controlled polymerization ofn-butylacrylate nitroxylether dodecylmercaptane (101), mol % (mol %)yield sample no. on monomer on monomer (%) M_(n) (calc) M_(n) M_(w)M_(w)/M_(n) comparison V1 1 — 23 3300 3300 4500 1.36 example E1 1 0.1 66 7100 8700 13100 1.5 example E2 1 0.25 85 9100 10500 16800 1.6

Under the same polymerization conditions a significant increase in yieldand molecular weight is observed, whereas the polydispersity (PD)remains low. The slight increase in polydispersity is due to the highermolecular weights achieved in examples E1 and E2.

Table 2 shows the result when the nitroxyl ether is partiallysubstituted by the chain transfer agent.

TABELLE 2 Influence of partial substitution of the nitroxylether bydodecylmercaptane on controlled polymerization of n-butylacrylate.nitroxylether dodecylmercaptane (101), mol % (mol %) yield sample no. onmonomer on monomer (%) M_(n) (calc) M_(n) M_(w) M_(w)/M_(n) comparisonV1 1 — 23 3300 3300 4500 1.36 E3 0.8 0.2 84 13500 11200 18200 1.62

A substitution of 20% nitroxyl ether by dodecylmercaptane leads to asignificant increase in yield and polydispersity remains narrow.

Reinitiating Examples E5 and E6 Using Macroinitiators Prepared in thePresence of a Nitroxyl Ether and a Chain Transfer Agent

2.5 g of the polymers prepared as samples no. V1 and E1 (denoted in thefollowing as macroinitiators, MI) and 7.5 g monomer are added to aSchlenk tube, flushed with argon and equipped with magnetic stirrer. TheSchlenck reactor is closed and the remaining oxygen is removed in twofreeze thaw cycles with liquid nitrogen. The tube is filled with argonand heated to 130° C. for 6 hours with stirring. The remaining monomeris removed under vacuum at room temperature. Drying is continued untilconstant weight of the residue. Molecular weight and distribution aredetermined using size exclusion chromatography with tetrahydrofurane andcalibrated with polystyrene standards. The results are given in Table 3.

TABLE 3 Block copolymerization with n-butylacrylate and styrene yield ofadded M_(w)/M_(n) monomer monomer sample MI M_(n) (MI) (MI) added (%)M_(n) M_(w) M_(w)/M_(n) comparison V1 3300 1.36 n-butylacrylate 22 56007100 1.27 V2 E5 E1 8700 1.50 n-butylacrylate 45 18500 26100 1.41comparison V1 3300 1.35 styrene 57 7800 10900 1.40 V3 E6 E1 8700 1.50styrene 59 20500 28500 1.39

The results in table 3 clearly show that the polymers (macroinitiators)prepared in the first step in the presence of a chain transfer agent(example E1) lead to higher yields and higher molecular weights whensubjected to a second block copolymerisation with eithern-butyl-acrylate or styrene as compared to the comparativemacroinitiator (example V1).

EXAMPLES E7-E14

Polymerization is carried out as described for examples E1-E3 usingn-butylacrylate and tert.-butylacrylate as monomers and compound 102 asnitroxylether. The thiol compound is 1-dodecylmercaptane orethylhexylthioglycolate.

The results are shown in Table 4 to 7.

TABLE 4 Influence of 1-dodecylmercaptane on the controlledpolymerization of tert.-butylacrylate nitroxylether thiol compound, mol% on mol % on yield sample no. monomer monomer (%) M_(n) (calc) M_(n)(GPC) M_(w) (GPC) M_(w)/M_(n) comparison 1 — 33 4500 4300 6100 1.4 V4 E71 0.1  56 7500 8400 12400 1.5 E8 1 0.25 67 8900 7600 11800 1.6

TABLE 5 Influence of ethylhexylthioglycolate on controlledpolymerization of n-butylacrylate nitroxylether thiol compound, mol % onmol % on Yield M_(n) M_(w) sample no. monomer monomer (%) M_(n) (calc)(GPC) (GPC) M_(w)/M_(n) comparison 1 — 32 4300 4300 5400 1.2 V5 E9 10.25 49 6600 6200 8200 1.3 E10 1 0.5  54 7300 6200 8400 1.4

TABLE 6 Influence of partial substitution of the nitroxylether byethylhexylthioglycolate on controlled polymerization oftert.-butylacrylate nitroxylether thiol compound, mol % on mol % onyield sample no. monomer monomer (%) M_(n) (calc) M_(n) (GPC) M_(w)(GPC) M_(w)/M_(n) comparison 1 — 33 4500 4300 6100 1.4 V4 E11 0.8 0.2 6310400 9700 13900 1.4 E12 0.7 0.3 61 11500 10400 14900 1.4

TABLE 7 Influence of partial substitution of the nitroxylether byethylhexylthioglycolate on controlled polymerization of n-butylacrylatenitroxylether thiol compound, mol % on mol % on yield sample no. monomermonomer (%) M_(n) (calc) M_(n) (GPC) M_(w) (GPC) M_(w)/M_(n) comparison1 — 32 4300 4300 5400 1.2 V5 E13 0.8 0.2 70 11600 11000 13600 1.2 E140.7 0.3 70 13100 10700 15800 1.5

In both sets of experiments, the replacement of a maximum amount of 30%(by mol) of nitroxyl ether still allows the controlled radicalpolymerization process to proceed with increased yield accompanied by apolydispersity value as low as measured for the reference sample.

Reinitiation Experiments using a Macroinitiator Prepared in the Presenceof a Nitroxyl Ether without the Addition of a Chain Transfer Agent(examples E15-E17). Table 8

Preparation of the macroinitiator (V6).

The macroinitiator (V6) is synthesized using 1 mol % nitroxyl ether 101in a 2 L autoclave at 120° C. The monomer, n-butylacrylate, is degassedby applying three consecutive vacuum-argon-flush cycles at roomtemperature, then the solution is heated rapidly to 120° C. whilestirring. The nitroxyl ether, dissolved in 50 ml of monomer, is added atonce when the final reaction temperature is reached. The polymerizationis allowed to proceed for 6 hours. After polymerization the residualmonomer is evaporated and the polymer dried in vacuo at 30° C. untilconstant weight is achieved. The macroinitiator V6 is a clear, slightlyorange viscous polymer. The overall yield is 40%. Molecular weights areanalyzed using SEC calibrated with polystyrene standards.

Reinitiation Experiments

In a 100 ml Schlenk tube, equipped with a magnetic stir bar, 10 g of V6are dissolved in 50 g distilled monomer (as listed in the table) untilthe macroinitiator is completely dissolved. Then, calculated amounts of1-dodecylmercaptane are added. Additionally, one experiment in eachseries is carried out without the thiol as a reference.

The tubes are degassed by three consecutive freeze-thaw-cycles andflushed with argon. Then they are immersed in an oil bath at 130° C. andthe polymerization is allowed to proceed. After 6 hours, residualmonomer is evaporated in vacuo and the polymer obtained dried at 30° C.in vacuo until constant weight is achieved. SEC analysis is performed onthe crude reaction products.

TABLE 8 Reinitiation experiments with different concentrations of thioladded amount of thiol added (estimation based on C—O—N yield (%) ofadded endgroups in added sample no. monomer macroinitiaor V6) monomerM_(n) M_(w) M_(w)/M_(n) macroinitiator 5500 7900 1.4 V6 comparisonn-butylacrylate 24 12500 15400 1.2 V7 E15 n-butylacrylate 35 mg 69 2170031000 1.4 E16 n-butylacrylate 70 mg 72 20300 30700 1.5 V8 tert.- — 1610600 13300 1.25 butylacrylate E17 tert.- 70 mg 66 18900 26000 1.4butylacrylate

From the data obtained it becomes evident that the concept of adding achain transfer agent to the controlled polymerization of vinylicmonomers in order to increase yield and molecular weight is not onlyvalid for a homopolymerization step, but also for any reaction step in amulti-step polymerization procedure.

Table 9 shows the results of a second reinitiation step. For theformation of a third subsequent polymerization a polymer listed in Table8 (E 15) was submitted to a consecutive polymerization routine withoutany additional thiol addition. SEC analysis proved the reinitiationability of the polymer.

Multiple Reinitiation Experiments (Examples E18-E19) Table 9

10 grams of the polymer E15 (n-butylacrylate/n-butylacrylate)synthesized in the presence of a chain transfer agent in the secondpolymerization step are added to 50 grams of pure monomer in a Schlenktube, equipped with a magnetic stir bar and dissolved. The tubes aredegassed by three consecutive freeze-thaw-cycles and flushed with argon.Then they are immersed in an oil bath at 130° C. and the polymerizationis allowed to proceed. After 6 hours, residual monomer is evaporated invacuo and the polymer obtained dried at 30° C. in vacuo until constantweight is achieved. SEC analysis is performed on the crude reactionproducts.

The molecular weight data prove that the third polymerization step issuccessful. Chain extension occurs, whilst maintaining molecular weightcontrol.

TABLE 9 Reinitiation experiments using a polymer (macroinitiator)obtained in the presence of a chain transfer agent yield (%) of sampleadded initial no. Comonomer monomer M_(n) M_(w) M_(w)/M_(n) polymerfinal polymer E15 21700 31000 1.4 nBuA-nBuA — E18 n-butylacrylate 3738700 62200 1.6 nBuA-nBuA nBuA-nBuA- nBuA E19 styrene 64 60400 83700 1.4nBuA-nBuA nBuA-nBuA-Sty

Table 10 shows the color improvement of the final product whenpolymerization is carried out in the presence of a chain transfer agent.

Preparation of comparative example V10 is identical to thepolymerization procedure as described before for n-butylacrylate inexample E1-E3, with the exception that dicumylperoxide is used asinitiator instead of nitroxyl ether (101) and no dodecylmercaptane isadded.

TABLE 10 nitroxylether Yellowness Index Dicumylperoxide, (101),dodecylmercaptane 5 measurements and average mol % mol % (mol %) valueof 5 are given sample on monomer on monomer on monomer #1 #2 #3 #4 #5avg. V1 — 1 — 7.27 6.58 6.52 5.32 4.56 6.05 E1 — 1 0.1 4.7 4.41 4.534.42 4.27 4.47 E2 — 1  0.25 3.95 3.7 3.66 3.79 3.57 3.73 E3 —   0.8 0.23.83 3.51 3.61 3.56 3.78 3.66 V10 1 — — 3.47 3.37 3.37 3.44 3.39 3.41 YIvalues were measured with a Minolta Spectrophotometer CM 3600d.

The results in table 10 show that the Yellowness Index of the polymersprepared according to the present invention is reduced compared to thepolymer obtained with the nitroxyl ether alone.

1. A polymerizable composition, comprising a) at least one ethylenicallyunsaturated monomer or oligomer, b2) at least one stable free nitroxylradical

and a free radical initiator and c) a chain transfer agent selected fromthe group consisting of a mercaptane and a thioether, wherein thenitroxyl radical of component b2) is of formula A′, B′ or O′

wherein m is 1, R is hydrogen, C₁-C₁₈alkyl which is uninterrupted orinterrupted by one or more oxygen atoms, cyanoethyl, benzoyl, glycidyl,a monovalent radical of an aliphatic carboxylic acid having 2 to 18carbon atoms, of a cycloaliphatic carboxylic acid having 7 to 15 carbonatoms, or an α,β-unsaturated carboxylic acid having 3 to 5 carbon atomsor of an aromatic carboxylic acid having 7 to 15 carbon atoms; p is 1;R₁ is C₁-C₁₂alkyl, C₅-C₇cycloalkyl, C₇-C₈aralkyl, C₂-C₁₈alkanoyl,C₃-C₅alkenoyl or benzoyl; R₂ is C₁-C₁₈alkyl, C₅-C₇cycloalkyl,C₂-C₈alkenyl unsubstituted or substituted by a cyano, carbonyl orcarbamide group, or is glycidyl, a group of the formula —CH₂CH(OH)-Z orof the formula —CO-Z or —CONH-Z wherein Z is hydrogen, methyl or phenyl;G₆ is hydrogen and G₅ is hydrogen or C₁-C₄alkyl, and G₁ and G₃ aremethyl and G₂ and G₄ are ethyl or propyl or G₁ and G₂ are methyl and G₃and G₄ are ethyl or propyl.
 2. A polymerizable composition, comprisinga) a macroinitiator, which is an oligomer or polymer prepared in thepresence of a nitroxyl radical and having attached to theoligomer/polymer backbone a nitroxyl group with the structural element

b) an ethylenically unsaturated monomer or oligomer and c) a chaintransfer agent selected from the group consisting of a mercaptane, athioether and a disulfide, wherein the structural element

of the macroinitiator is derived from a compound of formulae A′, B′ orO′

wherein m is 1, R is hydrogen, C₁-C₁₈alkyl which is uninterrupted orinterrupted by one or more oxygen atoms, cyanoethyl, benzoyl, glycidyl,a monovalent radical of an aliphatic carboxylic acid having 2 to 18carbon atoms, of a cycloaliphatic carboxylic acid having 7 to 15 carbonatoms, or an α,β-unsaturated carboxylic acid having 3 to 5 carbon atomsor of an aromatic carboxylic acid having 7 to 15 carbon atoms; p is 1;R₁ is C₁-C₁₂alkyl, C₅-C₇cycloalkyl, C₇-C₈aralkyl, C₂-C₁₈alkanoyl,C₃-C₅alkenoyl or benzoyl; R₂ is C₁-C₁₈alkyl, C₅-C₇cycloalkyl,C₂-C₈alkenyl unsubstituted or substituted by a cyano, carbonyl orcarbamide group, or is glycidyl, a group of the formula —CH₂CH(OH)-Z orof the formula —CO-Z or —CONH-Z wherein Z is hydrogen, methyl or phenyl;G₆ is hydrogen and G₅ is hydrogen or C₁-C₄alkyl, and G₁ and G₃ aremethyl and G₂ and G₄ are ethyl or propyl or G₁ and G₂ are methyl and G₃and G₄ are ethyl or propyl.
 3. A composition according to claim 1,wherein component c) is a compound of formula (IIa) or (IIb)R₃₀—S—H (IIa) R₃₀ —S—R₃₀ (IIb) wherein R₃₀ is C₁-C₁₈alkyl, C₃-C₁₈alkenyl, C₃-C₁₈alkinyl, (C₁-C₁₈)alkyl-O—(C₁-C₁₈alkylen)-,HO—(C₁-C₁₈alkylen)-, (C₁-C₁₈alkyl)₂N—(C₁-C₁₈alkylen)-,(C₁-C₁₈)alkyl-O—C(O)—(C₁-C₁₈alkylen)-, phenyl, phenyl(C₁-C₃alkyl),phenyl-C(O)— or (C₁-C₁₈alkyl)₂N—C(S)—.
 4. A composition according toclaim 3, wherein component c) is of formula (IIa) and R₃₀ isC₈-C₁₈alkyl.
 5. A process for preparing an oligomer, a cooligomer, apolymer or a copolymer (block, random or graft) with a polydispersity of1.1 to 2 by free radical polymerization of at least one ethylenicallyunsaturated monomer or oligomer, which comprises (co)polymerizing themonomer or monomers/oligomers in the presence of b2) at least one stablefree nitroxyl radical

and a free radical initiator and c) a chain transfer agent selected fromthe group consisting of a mercaptane and a thioether.
 6. A process forpreparing a block (co)polymer with a polydispersity of 1.1 to 2 by freeradical polymerization which comprises (co)polymerizing a) amacroinitiator, which is an oligomer or polymer prepared in the presenceof a nitroxyl radical and having attached to the oligomer/polymerbackbone a nitroxyl group with the structural element

b) an ethylenically unsaturated monomer or oligomer in the presence ofc) a chain transfer agent selected from the group consisting of amercaptane, a thioether and a disulfide; under reaction conditionscapable of effecting scission of the O-polymer bond to form two freeradicals, the polymer radical (macroinitiator) being capable ofinitiating polymerization.
 7. A process according to claim 5, whereinthe the nitroxyl radical of component b2) is present in an amount offrom 0.001 mol-% to 20 mol-%, based on the monomer or monomer mixture.8. A process according to claim 5, wherein the free radical initiator ispresent in an amount of 0.001 mol-% to 20 mol-%, based on the monomer ormonomer mixture.
 9. A process according to claim 6, wherein the scissionof the O-polymer bond is effected by heating and takes place at atemperature of between 50° C. and 180° C.
 10. A process according toclaim 5, wherein the chain transfer agent, component c), is present inan amount of from 0.001 mol-% to 0.5 mol-%, based on the monomer ormonomer mixture.
 11. A composition according to claim 2, whereincomponent c) is a compound of formula (IIa), (IIb) or (IIc)R₃₀—S—H (IIa) R₃₀—S—R₃₀ (IIb) R₃₁—S—S—R₃₁ (IIc) wherein R₃₀ isC₁-C₁₈alkyl, C₃-C₁₈ alkenyl, C₃-C₁₈alkinyl,(C₁-C₁₈)alkyl-O—(C₁-C₁₈alkylen)-, HO—(C₁-C₁₈alkylen)-,(C₁-C₁₈alkyl)₂N—(C₁-C₁₈alkylen)-, (C₁-C₁₈)alkyl-O—C(O)—(C₁-C₁₈alkylen)-,phenyl, phenyl(C₁-C₃alkyl), phenyl-C(O)— or (C₁-C₁₈alkyl)₂N—C(S)—; andR₃₁ is C₁-C₁₈alkyl, C₃-C₁₈alkenyl, C₃-C₁₈alkinyl,(C₁-C₁₈)alkyl-O—(C₁-C₁₈alkylen)- or HO—(C₁-C₁₈alkylen)-.
 12. Acomposition according to claim 11, wherein component c) is of formula(IIa) and R₃₀ is C₈-C₁₈alkyl.
 13. A process according to claim 6,wherein the chain transfer agent, component c), is present in an amountof from 0.001 mol-% to 0.5 mol-%, based on the monomer or monomermixture.
 14. A process according to claim 5, wherein the nitroxylradical of component b2) is of formula A′, B′ or O′

wherein m is 1, R is hydrogen, C₁-C₁₈alkyl which is uninterrupted orinterrupted by one or more oxygen atoms, cyanoethyl, benzoyl, glycidyl,a monovalent radical of an aliphatic carboxylic acid having ₂ to 18carbon atoms, of a cycloaliphatic carboxylic acid having 7 to 15 carbonatoms, or an α, β-unsaturated carboxylic acid having 3 to 5 carbon atomsor of an aromatic carboxylic acid having 7 to 15 carbon atoms; p is 1;R₁ is C₁-C₁₂alkyl, C₅-C₇cycloalkyl, C₇-C₈aralkyl, C₂-C₁₈alkanoyl,C₃-C₅alkenoyl or benzoyl; R₂ is C₁-C₁₈alkyl, C₅-C₇cycloalkyl,C₂-C₈alkenyl unsubstituted or substituted by a cyano, carbonyl orcarbamide group, or is glycidyl, a group of the formula —CH₂CH(OH)-Z orof the formula —CO-Z or —CONH-Z wherein Z is hydrogen, methyl or phenyl;G₆ is hydrogen and G₅ is hydrogen or C₁-C₄alkyl, and G₁ and G₃ aremethyl and G₂ and G₄ are ethyl or propyl or G₁ and G₂ are methyl and G₃and G₄ are ethyl or propyl.
 15. A process according to claim 10, whereinthe nitroxyl radical of component b2) is of formula (Ic′), (Id′), (Ie′),(If′), (Ig′) or (Ih′)

wherein R₁, R₂, R₃ and R₄ independently of each other are C₁-C₁₈alkyl,C₃-C₁₈alkenyl, C₃-C₁₈alkinyl, C₁-C₁₈alkyl, C₃-C₁₈alkenyl, C₃-C₁₈alkinylwhich are substituted by OH, halogen or a group —O—C(O)—R₅, C₂-C₁₈alkylwhich is interrupted by at least one O atom and/or NR₅ group,C₃-C₁₂cycloalkyl or C₆-C₁₀aryl or R₁ and R₂ and/or R₃ and R₄ togetherwith the linking carbon atom form a C₃-C₁₂cycloalkyl radical; R₅, R₆ andR₇ independently are hydrogen, C₁-C₁₈alkyl or C₆-C₁₀aryl; R₈ ishydrogen, OH, C₁-C₁₈alkyl, C₃-C₁₈alkenyl, C₃-C₁₈alkinyl, C₁-C₁₈alkyl,C₃-C₁₈alkenyl, C₃-C₁₈alkinyl which are substituted by one or more OH,halogen or a group —O—C(O)—R₅, C₂-C₁₈alkyl which is interrupted by atleast one O atom and/or NR₅ group, C₃-C₁₂cycloalkyl or C₆-C₁₀aryl,C₇-C₉phenylalkyl, C₅-C₁₀heteroaryl, —C(O)—C₁-C₁₈alkyl, —O—C₁-C₁₈alkyl or—COOC₁-C₁₈alkyl; and R₉, R₁₀, R₁₁ and R₁₂ are independently hydrogen,phenyl or C₁-C₁₈alkyl.